Oxygen evolution

Oxygen evolution is the chemical process of making oxygen gas (O₂) from reactions, usually using water. Water is very common in the universe and it contains oxygen. On Earth, oxygen is mostly made by living things through a process called oxygenic photosynthesis, as well as other natural processes like photodissociation and hydroelectrolysis.

This natural making of oxygen is very important for all complex life on our planet. Most living things need oxygen to get energy from food through a process called aerobic respiration. This need for oxygen started when complex cells evolved long ago, and it continues today because oxygen must be regularly replaced by photosynthesis.

In industry, making oxygen through chemical reactions can be difficult. Improving these reactions, especially a process called oxygen evolution reaction (OER), is important for creating new energy technologies. These include solar fuels, regenerative fuel cells, and metal–air batteries, which could help create a cleaner future.

Oxygen evolution in nature

Main article: Oxygen evolving complex

Plants and tiny water organisms called cyanobacteria make oxygen through a special process called photosynthesis. This happens when they use sunlight to break down water. The oxygen they make goes into the air we breathe.

This process needs special helpers, like a part called the oxygen-evolving complex that contains manganese. Other helpers, such as calcium and chloride, are also needed. The reaction looks like this:

2H₂O ⟶ 4e⁻ + 4H⁺ + O₂

The pieces from the water help make energy for the plant while the oxygen goes out into the atmosphere.

History of discovery

In the late 1700s, a scientist named Joseph Priestley found that plants could clean the air that had been used by a burning candle. He showed that the air cleaned by plants was safe for a mouse to breathe. Another scientist, Jan Ingenhousz, later discovered that this cleaning only happened when there was sunlight and green parts of the plant were present.

Water electrolysis

Together with hydrogen, oxygen is made during the electrolysis of water. This process helps store energy as hydrogen gas, which burns cleanly.

Electrons move from the cathode to make hydrogen gas. At the anode, water changes into oxygen gas and releases electrons to finish the circuit. This makes water break down into oxygen and hydrogen gas.

Chemical oxygen generation

Some special chemicals can release oxygen when heated. These are used in places like submarines and airplanes to give people oxygen if there is an emergency. One way to make oxygen is by heating a chemical called sodium chlorate, which changes into salt and oxygen gas:

2 NaClO₃ → 2 NaCl + 3 O₂

Another chemical, potassium permanganate, can also release oxygen when heated, but it makes less oxygen:

2 KMnO₄ → MnO₂ + K₂MnO₄ + O₂